The invention relates to an apparatus involving the potential measuring technique, and comprising an objective lens for focusing of primary electrons onto an object, and further comprising a spectrometer for the energy selection of secondary electrons.
Up until now, in commercial scanning electron microscopes, an electrostatic spectrometer for quantitative potential measurements was installed between the last lens (objective) and the target (H. P. Feuerbaum, Scanning Electron Microscopy/1979/I, 285-296 and U.S. Pat. Nos. 4,277,679 and 4,292,519), incorporated herein by reference. A spectrometer for the quantitative potential measurement requires a minimum working distance which prevents a reduction of the objective-focal length and hence a reduction of the lens aberrations.